Yes this should be posible with the correct configuration, however you will need to 2nd Modem to act as the gateway as the 618 cannot route itself plus DHCP will be diabled.
The problem here is needing to use the wifi from the Huawei. The 618 will route all traffic to itself as gateway even if you disable dhcp.
Disable wifi and dhcp on the Huawei. Set up a static IP of 192.168.8.2/24 on the 2nd Modem and associated default route. Configure 192.168.8.2 as DMZ on the Huawei. Then run everything from the 2nd Modem, including WiFi if it has built in.
This is a general rule however custom settings may apply depending on your setup/hardware as this is an advanced configuration and may affect your network speed.
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